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The development of thermomechanical coupled simulations for rolling contacts is challenging when the adjacent material is temperature-dependent or when there are cracks or other discontinuities on the contact surface. This paper proposes a novel thermomechanical coupled modeling method for rolling contacts using a nonlocal peridynamic (PD) approach. Fully coupled, ordinary state-based PD thermomechanical equations for the plane strain and plane stress cases are derived based on the strain-energy density, including thermal coupling terms, and detailed information on each parameter is provided. Subsequently, an algorithm for rolling thermal contacts in PD is proposed based on the penalty method. This study further provides a detailed modeling process and an algorithm for the proposed method based on a multi-rate time-integration scheme for numerical implementation. A typical two-dimensional (2D) wheel–rail rolling contact model is established to evaluate the performance of the proposed contact modeling method in wheel–rail thermal contact and to analyze the influence of temperature-dependent material and rail-surface cracks on the thermomechanical response. It is found that the contact stress and rail-surface temperature rise in the case of small creepages and temperature-independent materials are in good agreement with the analytical solution. In the case of large creepages, the mechanical and temperature results of using temperature-dependent materials and temperature-independent materials are quite different, and the frictional heat generated can cause martensitic transformation of adjacent materials. Rail-surface cracks cause a sharp increase in the contact stress and temperature rise near the cracks, and the high temperature also promotes crack growth. • A nonlocal thermomechanical coupled modeling method for rolling contacts using peridynamic is proposed. • Fully coupled, ordinary state-based PD thermomechanical equations are derived. • An algorithm for rolling thermal contacts in PD is proposed based on the penalty method. • A typical 2D wheel–rail rolling contact model is established for a case study. [ABSTRACT FROM AUTHOR]

Copper impregnated carbon/carbon composite (Cu-C/C composite) was fabricated for novel sliding collector material by weaving carbon fiber, heat treatment and Cu alloy impregnation. The effects of counterpart materials (Fe ball and Cu ball) on friction and wear behaviors were investigated and compared with the result of carbon contact strip used in high-speed railway. Morphology, chemical composition, phase and structure of wear surface and tribolayer were characterized to clarify tribological mechanisms. The results show that friction coefficient follows the order: Cu-C/C composite/Cu ball > carbon contact strip/Fe ball > Cu-C/C composite/Fe ball > carbon contact strip/Cu ball. The carbon crystalline of wear surface appears preferred orientation along the sliding orientation, which is benefit for boundary lubrication. When the counterpart material is Fe ball, Cu-C/C composite is superior to pure carbon strip in mechanical strength, electrical conductivity, wear resistance and friction performance. [ABSTRACT FROM AUTHOR]

• High cyclic tensile stress is the reason for the RCF damages in LPQ prepared hardened spots. • LPQT can prepare discrete hardened spots surrounded by transitional zone. • The transitional zone helps to alleviate the RCF damages in the hardened spot by decreasing the cyclic tensile stress. • RCF and wear resistances of the LPQT treated rail steel can be balanced by decreasing the transitional zone's thickness. Surface layer with heterogeneous microstructures (SLHM), characterized by hardened spots discretely embedded in a soft substrate, can be prepared by laminar plasma quenching (LPQ) to improve the wear resistance of the railway rail. However, severe rolling contact fatigue (RCF) cracks and spalling would occur in the hardened spots that only consist of quenched microstructure. This study analyzed the RCF damage mechanism of the LPQ prepared hardened spots by contact simulation. To improve the RCF resistance while maintaining the high wear resistance of the treated rail, a novel SLHM, whose discrete hardened spots are surrounded by transitional zone with the hardness lower than that of the quenched zone but higher than that of the substrate, was proposed and prepared by laminar plasma quenching-tempering (LPQT). Then, twin-disc tests and contact simulations were conducted to investigate the wear and RCF resistances of the LPQT treated rail steel. Results showed that the cause of the severe RCF cracks and spalling at the entry side of the LPQ prepared hardened spots was that the cyclic tensile stress at the entry side was always higher than that at the exit side under the cyclic rolling contact loading. The high tensile stress at the entry side of the LPQ prepared hardened spots resulted from the elastic deformation induced by tensile plastic deformation of the neighboring substrate. When the thickness of the transitional zone was about 0.1 mm, the generation of severe RCF cracks and spalling was significantly inhibited in the LPQT prepared hardened spots because the transitional zone decreases the cyclic tensile stress at the entry side of the quenched zone. Besides, the wear loss of such LPQT treated rail steel was only increased by 18.1 % compared with that of the LPQ treated rail steel, indicating that the wear resistance of the LPQT treated rail steel was not significantly reduced. These findings are promising for designing the microstructure of the surface layer to obtain wear-resistant rail with high RCF resistance. [ABSTRACT FROM AUTHOR]

• Increasing turbine rotor sizes have made main bearing reliability a major concern in modern turbines. • Industry and academia have played critical roles in improving the performance and service life of turbine main bearings. • Scholarly contributions have predominantly focused on the fields of bearing geometry and profile optimization. • Tapered roller bearings have received the most research attention compare to spherical roller bearings. • The authors recommend increased exploration of evolutionary bearing geometry optimization techniques. The growing demand for renewable energy has made wind turbines increasingly large and complex. Demand for efficient main bearings optimized to endure dynamic and unpredictable stresses while allowing turbine motion rises even more. Over the years, rolling element bearings have advanced to meet this demand, driven by innovations from industry and academia. This study examined industry-related and academic contributions to the advancement of wind turbine main bearings. Spherical and tapered roller bearings are identified as the basic wind turbine rotor bearings. From the works reviewed, it was found that industry-related contributions on these bearings center on bearing configuration improvements, cage improvements, the development of improved coats, and the design of novel evolutionary variants of the bearings. The SKF was identified as having contributed more to the development of wind turbine rotor bearings with the patenting of two novel bearings: the CARB toroidal bearing and the Nautilus. Scholarly contributions have majored in bearing geometry and profile optimization. Tapered roller bearings were found to have received more research attention than spherical roller bearings. Also, few innovative studies on CARB toroidal bearing, asymmetrical spherical roller bearing, and the Nautilus have been reported. Exclusively theoretical analyses have been mostly used in performance optimizations of the bearings. Only in a few studies did experimental investigations validate theoretical findings, creating potential avenues for experimental studies. Insights from the review indicate that tapered roller bearings or plain bearings could be viable substitute for spherical main shaft bearings, considering their persistent reliability challenges. The authors recommend more exploration of evolutionary bearing optimization techniques, more investigations on bearing lubricants, housing material, cage material, and coating material designs, and increased industry-academic engagement to pave the way for more main bearing innovation. [ABSTRACT FROM AUTHOR]

• Verified frog crack growth model combines impact simulation and fracture analysis. • Crack location and angle are more influential than train speed and axle load. • Observed accelerated growth of transverse cracks near the frog nose. • Proposed inspection strategy based on crack type, cumulative tonnage, and headway. Fatigue cracking is one of the notable failure mechanisms of railway turnout frogs due to high contact forces induced by the wheel-rail impact. However, the treatments specific to the frogs of cast high manganese steel to prevent sudden failure are rarely provided and are independent of the crack conditions, which can significantly affect the fatigue crack growth rate. To address this shortcoming, the fatigue crack growth in a cast high manganese steel frog is computationally investigated with varied wheel and crack conditions. The dynamic wheel-frog impact is first simulated to obtain the distribution of contact pressure imposed on the frog, and the propagation of the fatigue crack is then predicted using the finite element formulation in fracture mechanics. The simulation results show that the train speed and axle load can change the maximum contact stress. Nevertheless, when representing the growth rate in terms of the cumulative passing axle load, the effect of axle load and train speed on the crack growth is minimal and moderate, respectively. In contrast, the initial crack conditions, including the location and angle, have an overweighted influence. As a result, an inspection scheduling strategy for identified cracks with different conditions is proposed to consider both safety and operational efficiency. [ABSTRACT FROM AUTHOR]

• Three dynamic indicators for predicting plastic flow in railway systems based on the mechanics of wheel-rail contact, Tresca's yielding criterion and shakedown theory. • A dynamic method that is simple to model and fast to compute for predicting plastic flow in railway systems. • Key parameters affecting plastic flow and rolling contact fatigue. • A dynamic approach for the impact of plastic flow on rolling contact fatigue damage. • Effect of different degrees of plastic flow on rolling contact fatigue. To analyze the plastic flow of wheels and its impact on rolling contact fatigue (RCF), this article proposes a multibody dynamics approach that is simple to model and fast to compute, based on the mechanics of wheel-rail contact and Tresca yield criterion. This method is used to study the plastic flow of the wheels and is validated by comparing it with plastic flow analysis based on the shakedown theory. The study shows that the dynamics indicators of maximum shear stress, adhesion saturation and stress ratio effectively reflect the plastic deformation of the wheel. Additionally, increasing wheel speed and curve radius, and decreasing wheel-rail friction coefficient, can effectively reduce the area and severity of plastic deformation in the wheel. Ignoring the impact of temperature effects on RCF, it is found that the more severe the plastic flow, the greater the likelihood of RCF. That is, alleviating the plastic flow of the wheel can reduce RCF damage in wheels. This approach to managing the health of wheels provides a comprehensive understanding of the interplay between operational parameters and the mechanical behavior of wheel materials, guiding maintenance strategies and operational decisions to enhance safety and extend the lifespan of railway components. [ABSTRACT FROM AUTHOR]

• The hardness of the soft zone is much lower relative to the hardened surface of the raceway. • A hierarchical finite element modeling method of the main bearing is proposed. • The principle of selecting the optimum hardened depth is given. • The effect of the soft zone on the contact characteristics and fatigue life of the raceway is investigated. • This analyzing method can quickly and efficiently clarify the contact state in the soft zone during the rolling process. A hierarchical finite element modeling method is proposed to study the problem of fatigue spalling easily due to low hardness in the soft zone for the main bearing of a tunnel boring machine. Quasi-static analyses of the main bearing are performed based on the global symmetric model and verified by relative displacement tests of the rings. The invariant contact pressure is replaced by the rolling contact of the rollers in the local sub-model. The contact load is used as an input to solve the stress field, and then the effects of soft zone and hardened depth on the contact characteristics and fatigue lifetime of the sub-model are investigated. The results show there are stress peaks at the junction of the hardened and soft zones. The effect of hardened depth on the stress distribution and fatigue lifetime is relatively small. However, the optimum hardened depth is influenced by the contact load and the permissible stress of the material. The minimum lifetime of the raceway during rolling occurs in the soft zone. This paper achieves a fast and effective rolling contact fatigue analysis of the main bearing, which provides a theoretical basis for optimizing the main bearing design. [ABSTRACT FROM AUTHOR]

Rolling element bearings typically operate with fluctuating speed, leading to nonstationary vibrations. Moreover, bearings vibration signals are frequently hidden by strong distributions, making it difficult to detect clear bearing fault characteristics for diagnosis. Under this circumstance, the key issue is effectively extracting the transient features from the background interference and highlighting the time-varying fault characteristics. To address this issue, a sparse and low-rank decomposition approach is proposed. In this study, the sparsity of the variable defective characteristics and low-rank of background interference is revealed and exploited for bearing fault detection. Firstly, the time–frequency representation (TFR) of the envelope of measured signal is generated by the time–frequency transform. Then, a sparse and low-rank decomposition model is established based on robust principal component analysis (RPCA) to denoise the measured time–frequency representation and gain the sparse component. Finally, a time–frequency reassignment strategy is utilized to further enhance the capability of detecting the faulty characteristics in the decomposed sparse TFR. The synthetic and actual signals are evaluated to illustrate the reliability and efficacy of the proposed technique. The superiority is also validated by comparisons with STFT, synchrosqueezing transform (SST), ridge extraction method, and scaling-basis chirplet transform (SBCT). • A sparse and low-rank decomposition of time–frequency representation method is proposed for bearing fault diagnosis. • The sparsity of the time-varying fault characteristics and the low-rank property of noise are revealed for the first time. • The strong background interference can be well removed to highlight the fault features. • The effectiveness of the proposed method in simulated signal and actual situation is validated. [ABSTRACT FROM AUTHOR]

Inspired by the surface structure of lotus leaves, micro–nano hierarchical surface structures have been widely used for designing superhydrophobic surfaces. However, the conventionally designed superhydrophobic surface structures are fragile. In this study, a layer of micron-sized mullite whiskers was grown using molten salt on the surface of BaAl 2 Si 2 O 8 (BAS) glass ceramics. Subsquently, SiO 2 nanoparticles modified with 1H,1H,2H,2H-perfluorodecyltriethoxysilane were sprayed onto the whisker layer to form a superhydrophobic surface. The nanoparticles exhibit superhydrophobicity, which is protected by the whisker layer containing pores and bulges. This prohibits direct contact between the nanoparticles and external objects. Contact and rolling angle tests indicated that the surface contact angle of the micro–nano hierarchical structure is 158° and the rolling angle is less than 10°. The stability of the superhydrophobic surface was tested through ultraviolet light, long-time immersion in solutions with various pH values, water scouring, and sandpaper abrasion. The results showed that the contact angle is greater than 150°. This study is expected to provide a simple and effective method for fabricating superhydrophobic surfaces on ceramics on a large scale. [ABSTRACT FROM AUTHOR]

• A thermomechanically coupled peridynamic model for simulating wheel idling was established. • A dynamic simulation was conducted on rail wear during wheel idling. • The peridynamic model has the potential to provide wear coefficients for classical wear models. • The thermomechanical damage mechanism of rails during wheel idling was discussed. Wheel idling is an extreme sliding contact scenario that accelerates rail failure. Using temperature-dependent elastoplastic materials, a peridynamic (PD) model for wheel-rail contact was developed to investigate the thermomechanical damage behavior of rails during wheel idling. Numerical simulations of loading and unloading during wheel idling under different loads were performed, and the results of contact stress, temperature, plastic deformation, and material damage were obtained and analyzed. During loading, the temperature of the rail surface increases rapidly to over 1200 °C, which is well above the austenitization temperature. The intense thermal softening caused by high temperatures deteriorates the wheel-rail contact relationship and leads to a surge in plastic deformation. The softened surface material was continuously removed by the contact load, leading to severe wear damage, and the wear depth increased significantly with the load and idling time. The wear coefficients for the Archard wear model were derived using the wear results from the PD model. During unloading, the surface material cools rapidly at a rate of 1400 ° C / s through heat transfer into the rail, undergoing martensitic transformation and forming a brittle and hard white etching layer. The thickness of the WEL decreases as the wear depth increases. [ABSTRACT FROM AUTHOR]

• A 3D FE model of wheelset-turnout-sleeper structure is established. • The ratcheting effect of turnout material is simulated. • A mixed implicit-explicit FE method is used to simulate the wheelset passing through the turnout. • The transient contact behavior of high-speed turnouts under cyclic loading is investigated. • The evolution of ratcheting strain of rail under different numbers of cycles and crossing speeds is discussed. The present work introduces a three-dimensional finite element model for the wheel-turnout-sleeper system, incorporating a cyclic constitutive model that accurately captures the nonlinear hardening behavior of rail steel under cyclic loadings. At the same time, a mixed implicit-explicit finite element method is employed to investigate the transient rolling contact behavior of wheel-turnout. Through dynamic analysis, the transient rolling contact status of the wheel-turnout, stress and strain responses of the turnout, and wheel-rail forces are investigated under varying crossing speeds and number of cycles. It is found that during the wheelset crossing, the contact stress remains relatively stable on the stock rail, and multi-point contact occurs at the wing rail and long point rail, and the contact stress on the surface of the long point rail is more significant. With an increase in crossing speed in the same cycle, there is a gradual rise in contact stress on the long point rail face. At the same crossing speed, with the increase in the number of cycles, the contact position between the wheelset and the long point rail gradually moves back, and the top width of the contact position gradually expands. Meanwhile, the fluctuation range of vertical displacement of the wheel center diminishes, and the wheel flange moves away from the long point rail. Additionally, a progressive accumulation of ratcheting strain is observed on the rail, and the ratcheting strain on the long point rail significantly exceeds that on the stock rail. The research results will help to provide a reference for the optimization and design of the critical cross-section profile of the long point rail and will have guiding significance for the maintenance and repair of turnouts. [ABSTRACT FROM AUTHOR]

• Typical factors affecting the wheel-rail dynamic response are comprehensively considered to reveal the short-term load characteristics of frog under complex conditions. Meanwhile, based on the ellipsoidal Gaussian extrapolation theory, long-term wheel-rail load characteristics are obtained. • Combined with the strain energy fatigue parameter theory, a prediction method for the fatigue life of nose rail under complex conditions based on load spectrum preparation was proposed. • The location between the 30 mm and 35 mm sections of the nose rail has the shortest rolling contact fatigue crack initiation life and should be focused on during damage inspection. The rail profile irregular variation and wheel-rail relationships complexity at the gap in the frog enhance the wheel-rail impact forces, frequently resulting in rolling fatigue damage under complex cyclic loads. Therefore, it is particularly important to study the transient rolling contact load characteristics of fixed frog and to compile load spectrum considering various complex conditions for analyzing the fatigue damage of frog and extending the service life of structure. In this paper, a 3D transient FE model of wheelset and fixed frog is established, revealing rolling contact behavior of wheel-rail in frog area from both macro and mesoscopic perspectives. In order to investigate long-term load characteristics of wheel and rail under complex service conditions, the changes of line conditions, load conditions, rail wear state and other influencing factors in actual operation are taken into account. Based on elliptic Gaussian kernel density theory, a method for compiling the load spectrum of fixed frog nose rail is proposed, and the FP method is used for fatigue crack initiation life prediction of nose rail in fixed frog. The results show that the force state is more severe when passing through the frog in straight reverse direction, and resonance is prone to occur in the third and fifth vertical bending modes of the frog, as well as the fourth and sixth vertical bending modes of the stock rail. The increase in factors such as speed, axle load, wheelset lateral displacement towards frog side and wing rail wear will exacerbate wheel-rail impact and shorten frog service life. Different factors have an impact on the overall amplitude, oscillation center range, and maximum frequency load of the wheel-rail force in the long-term load spectrum of the frog. The fatigue crack initiation area of nose rail is mainly in 30 mm–35 mm sections, which is consistent with the on-site flaw detection results, verifying the accuracy of the calculation method developed in this paper. [ABSTRACT FROM AUTHOR]

• Generation arc is subjected to triple acceleration of P - v - I. • Surface damage is a combination of mechanical and electrical damages after arcing. • Conductive AFM visually confirm the harmful effects of oxidation on conductivity. This study employs copper (Cu)-Cu rolling pairs to investigate the failure characteristics and surface damage mechanism of current-carrying tribological contacts under various conditions (contact load P = 40–180 N, rotation speed v = 4–600 rpm, and current I = 0–2.5 A). Based on synchronous current curves and video observations, the severe current fluctuations caused by the electric arc can be considered a criterion for the failure of rolling electrical contacts. Surface damage assessment through scanning electron microscopy, X-ray photoelectron spectroscopy, and atomic force microscopy (AFM), reveal ablation pits, oxidation, and roughening as primary manifestations of electrical damage. Post-rolling, the Cu on the surface was oxidized to copper (II) oxide. As the degree of oxidation increased, the conductive area in the AFM current map decreased significantly at a sample bias voltage of 1.5 V. Notably, arc generation was subjected to the triple acceleration of the contact load, rotation speed, and current. A back propagation (BP) neural network model was established to predict the running cycles before arc generation. Based on independent validation experiments under P = 120 N, I = 1.0 A, v = 400, and 600 rpm, the average prediction error of the proposed BP neural network model was 8.13 %. The results of this study facilitate the understanding of failure mechanism and predicting life cycles of rolling electrical contacts. [ABSTRACT FROM AUTHOR]

• Local quenching causes gradient distribution of microstructure and hardness in wheel. • The statistical correlation is: Hardness = −2.77 × Fraction of proeutectoid ferrite + 328.07. • Wear and rolling contact causes microstructure evolution of wheel. • Microstructure and hardness show a significant synergistic evolution law. High-speed train wheels have complex service environments during wheel–rail contact, and a comprehensive understanding of the microstructural inhomogeneity at the rim is critical for service safety assessment. The local quenching process in the vicinity of the rim will cause a difference in microstructure, directly affecting the service performance of the material. In this study, high-throughput characterization method based on material genome engineering was used, the methods for characterising and identifying the microstructure of wheel steel were developed using high-throughput scanning electron microscopy, and the accuracy and reproducibility of the methods were evaluated. A point-to-point research scheme for microstructure image and hardness data was designed based on the concept of statistical mapping characterization. The area fraction of the proeutectoid ferrite and micro-Vickers hardness distribution in a large size range of the key area of the rim and their internal correlation was obtained, these helped avoid statistical and representativeness limitations of traditional local selection analysis of microstructure and hardness. The results indicates that the area fraction of proeutectoid ferrite and micro-Vickers hardness showed a clear gradient distribution, and opposite distribution trend, with a high negative correlation. In addition, by observing the correlation between microstructure and hardness, and studying the evolution of microstructure, it was found that the microstructure and hardness of the rim near the tread demonstrated a significant synergistic evolution law under the influence of service, this was observed both statistically and microscopically. These findings enhanced the application prospects of the microstructure-performance statistical mapping method, and were beneficial in efficiently evaluating the service life and safety of key components. [ABSTRACT FROM AUTHOR]

[Display omitted] • A completely non-assembly steerable grasper in titanium was fabricated by additive manufacturing. • Miniature lattice structures were used as compliant flexures. • Deflection tests of different lattice designs were performed as characterization. • Lattice flexures were applied in the design of rolling joints with different configurations. • The final grasper design is low-friction and does not require any post-processing steps. Metal additive manufacturing is a promising technology for the production of functional medical products, due to its high shape complexity and resolution, and ability to withstand sterilization temperatures. This study explores the possibility of designing a completely non-assembly steerable surgical instrument using Selective Laser Melting. Despite its advantages for medical devices, the rough surface quality of unfinished parts can be problematic for non-assembly designs, leading to increased friction and wear in rigid body mechanisms and tendon-actuated mechanisms. We investigated printing of rolling contact joints with crossed flexures as low-friction joints, adjusted for printing in titanium for the design of the instrument. Grid-based lattice structures were incorporated as miniature flexures, and we explored the influence of various grid sizes on the flexibility and bending stiffness of the lattices. Based on this exploration, we altered the rolling joint configuration from two crossed flexures to a single straight flexure for our design. The resulting steerable surgical instrument design is completely non-assembly, including its actuation, facilitates easy removal of support structures, and requires no surface finishing steps. It has a diameter of less than 20 mm, facilitates opening and closing of a grasper, and steering of the grasper by 20 degrees. [ABSTRACT FROM AUTHOR]

• A universal rotor-bearing-disk system model is established. • The model considers three types of maneuvering loads. • The special vibration responses of the system under rolling, pitching and yawing maneuver loads are compared and analyzed. It is an important embodiment of fighter's comprehensive ability to have high maneuverability. Therefore, it is necessary to study the coupling dynamic behavior of rotor system in typical maneuvering flight. Based on the finite element method, a 6-node rotor-bearing-disk system model with three kinds of maneuvering loads, nonlinear contact force of rolling bearing, eccentric unbalanced force of disk and gravity field is established in this paper, and the dynamic responses of the system under rolling, pitching and yawing maneuvering is analyzed in detail. The Newmark-β method is used to solve the system model. The system responses under different rotation speeds and two given rotation speeds are mainly analyzed. The system responses under three kinds of maneuvering loads are compared and analyzed. Finally, the 7-node stepped shaft system model is used to verify the universality of the analysis results in this paper. It is found that, under the same maneuvering load value, the possibility of rub-impact and frequency division components caused by different flight modes are different. The research in this paper can provide a cognitive basis for the mechanism of system rubbing fault under different maneuvers. [ABSTRACT FROM AUTHOR]

Intelligent fault diagnosis of rolling element bearings gains increasing attention in recent years due to the promising development of artificial intelligent technology. Many intelligent diagnosis methods work well requiring massive historical data of the diagnosed object. However, it is hard to get sufficient fault data in advance in real diagnosis scenario and the diagnosis model constructed on such small dataset suffers from serious overfitting and losing the ability of generalization, which is described as small sample problem in this paper. Focus on the small sample problem, this paper proposes a new intelligent fault diagnosis framework based on dynamic model and transfer learning for rolling element bearings race faults. In the proposed framework, dynamic model of bearing is utilized to generate massive and various simulation data, then the diagnosis knowledge learned from simulation data is leveraged to real scenario based on convolutional neural network (CNN) and parameter transfer strategies. The effectiveness of the proposed method is verified and discussed based on three fault diagnosis cases in detail. The results show that based on the simulation data and parameter transfer strategies in CNN, the proposed method can learn more transferable features and reduce the feature distribution discrepancy, contributing to enhancing the fault identification performance significantly. • A bearing diagnosis framework via simulation auxiliary and parameter transfer for small sample problem. • Exploring effectiveness under diverse transfer strategies. • Leveraging transferable knowledge from simulation data to real scenario. • Robust to CNN architectures with different complexity. [ABSTRACT FROM AUTHOR]

Incipient fault detection of rolling bearings is a challenging task since the weak fault features are disturbed by heavy background noise. This paper develops a periodicity-enhanced sparse representation method to address this issue. Firstly, periodicity-enhanced basis pursuit denoising (PBPD) is proposed by the theoretical derivation. Fault proportion is defined to quantify the single fault severity of sparse signals, then a periodicity-decision criterion for determining the optimal potential fault period is designed to periodically filter the last sparse signal. Secondly, the suitable linear transformation for PBPD is investigated in comparison and maximal overlapping discrete wavelet packet transform is adopted eventually. Thirdly, adaptive selection strategies are developed for the key parameters of PBPD. Simulations and experimental verifications demonstrate PBPD's excellent performance in rolling bearing incipient fault detection. • PBPD for detecting incipient fault from heavily noise-polluted signals is proposed. • MODWPT is adopted as the linear transformation for PBPD. • A reliable periodicity-decision criterion is designed for PBPD. • Adaptive selection strategies are developed for the key parameters of PBPD. • Detailed simulation and experiments validate the effectiveness of PBPD. [ABSTRACT FROM AUTHOR]

• A new method for elasto-plastic contact pressure distribution of elliptical, circular and line contact is proposed. • The proposed method is suitable for different contact materials, contact-body's sizes and normal external loads. • The prediction accuracy and applicability of the proposed method are verified. According to the Hertz's contact theory (HCT) and considering the strain hardening of materials, an effective calculation method is proposed for solving the elasto-plastic contact pressure and the contact patch size under arbitrary smooth and continuous contact conditions. Firstly, it is assumed that the outer and inner edges of the contact patch are elastic and elasto-plastic contact zones, respectively, the contact pressure in the elastic contact zone satisfies the HCT, while the contact pressure in the elasto-plastic contact zone is the superposition of a constant contact pressure and several small ellipsoidal distribution contact pressures. Then, the explicit expressions of contact patch size and contact pressure under the elasto-plastic elliptical, circular and line contact conditions are derived, respectively. Subsequently, the accuracy and applicability of the proposed method are evaluated by comparing the predicted results with the finite element simulations. Finally, the accuracy of the proposed method is further verified by comparing the predicted results with the typical results in literature. It is shown that the proposed method has high calculation accuracy, and the maximum relative errors are 9.32% for the elliptical contact, 4.61% for the circular contact and 11.84% for the line contact, respectively. Meanwhile, the proposed method can effectively predict the contact pressure distribution under the elasto-plastic elliptical, circular and line contacts, and shows a general applicability for different contact materials, contact-body's sizes and normal external loads, as well as for the elasto-plastic wheel-rail contact analysis. [ABSTRACT FROM AUTHOR]

• Based on the Hertzian contact distribution and creep-slip characteristics, the fatigue life of spinning bearings is predicted using the damage parameter theory of the critical plane method and the L-P theory. • The deviation rate between the finite element simulation and the theoretical calculation results is 6.61% • The rotation speed, friction coefficient and external load affect the fatigue life of spinning bearings, and better lubrication and excellent contact surface to extend the life. • A rotary bearing life experimental device verified the reliability of the theoretically calculated deviation rate is 3.86%. In order to ensure the longer working life of rolling guide bushing, this work proposed a fatigue life prediction model of spinning bearings based on the Hertzian contact distribution and creep-slip characteristic. The influence of different parameters on the fatigue life of spinning bearings was analyzed according to the damage parameter theory of the critical plane method and the L-P theory. Finally, the fatigue life prediction model of spinning bearings was verified through the finite element simulation combined with the experiments. The reliability results show that creep-slip characteristic and deformation lead to the contact zone stress of the spinning bearing firstly increases, decreases subsequently to zero and then increases to the peak value. The increase of rotational speed will make the fatigue life of the spinning bearing firstly increases and then decreases. With the increase of friction coefficient, its fatigue life will become smaller and smaller, and the increase of the external load will decrease its fatigue life. Meanwhile, the prediction error rate of the fatigue life prediction model proposed in this study is 4.60%, which is within the error tolerance. This study provides certain methods and ideas for fatigue life prediction of spinning bearings, and lays a theoretical foundation for the design of highly reliable spinning bearings. [ABSTRACT FROM AUTHOR]

The construction of rack railways is widely planned across the mountainous areas of Southwest China. However, the huge differences in the daytime and nighttime temperatures in these areas easily lead to deformation mismatch between rack and bridge structures and subsequently result in unpredictable phenomena, such as connection failures in the rack system. This article then explores the vehicle-track (rack)-bridge system (VTRBS) interaction problem caused by extreme temperature loads. Guided by train-track-bridge dynamic interaction theory and considering the meshing behavior of the gear-rack and wheel-rail contact, a dynamic model for investigating the VTRBS interaction under extreme temperature load is constructed. The reliability of the rack system on a super-slope bridge under different rack and sleeper connection modes is studied using this model, and the modified connection mode is proposed. Under an extreme temperature load of –45 ℃, the reliability of the rack system is greatly affected by the rack and sleeper connection modes. When traditional fixed connections are used, the maximum stresses in the rack and fixed connection bolts are 1095 MPa and 1980 MPa, respectively, both exceeding the material strength. When using traditional fasteners, the maximum stresses in the rack and fastener bolts are 203 MPa and 38 MPa, which do not exceed the material strength. However, the elastic displacement between the rack and sleeper exceeds the allowable range of traditional fasteners. When using longitudinal resistance modified fasteners, the stresses in the rack system do not exceed the material strength, but the elastic displacement exceeds the maximum allowable range. When using elastic displacement modified fasteners, the modified elastic displacement ranges between 16 mm and 24 mm, which is within the normal working range. When using longitudinal resistance and elastic displacement modified fasteners, the modified elastic displacement ranges between 12 mm and 24 mm, which is also within the normal working range. These results provide theoretical basis for the early design and later operation and maintenance of rack railways. • The theoretical model of vehicle-track (rack)-bridge system is established considering temperature load. • The mechanical properties of the rack system under five different connection modes are studied. • Modified fasteners suitable for rack railways on bridge under extreme temperature load are proposed. • The normal working range of modified fasteners under extreme temperature load is provided. [ABSTRACT FROM AUTHOR]

• First S-N curve of surface initiated damage under rolling contact fatigue. • Uniquely conservative mechanical fatigue failure definition used for surface damage. • RCF and torsional fatigue S-N curves have similar fatigue strength exponent. • Study unveils that torsion tests can predict RCF surface damage results 10x faster. • Different operating regimes identified based on RCF surface damage severity. This paper presents fundamental findings on equivalence of rolling contact fatigue (RCF) driven surface damage and torsional fatigue modes of failure. Fatigue experiments were conducted for both modes of failure using AISI 4130 case carburized steel specimens. A Thrust Bearing Surface Pitting Rig (TBSPR) was designed and developed to perform RCF tests on flat test specimens using thrust ball bearings. The experiments were conducted in boundary lubrication regime, simulating the contact conditions in tribological machine components. The current investigation presents a novel approach where the effect of contact pressure and number of fatigue cycles on the initiation of surface damage was characterized by surface profilometry of the wear track after each test to generate a stress-life (S-N) map. The S-N map provides unique insights to early detection of RCF driven fatigue damage. The S-N map was utilized to generate the surface damage S-N curve. Torsional fatigue experiments were conducted on the same material, and the S-N curves of both failure modes were compared. The comparison shows key similarities between the two S-N curves, as they differ by a simple scaling factor. This investigation demonstrates that RCF driven surface damage characteristics can be predicted by conducting much simpler, and faster, torsion fatigue tests. This paper also presents a novel methodology to determine contact pressures to avoid incipient micropitting/microdenting damage. [Display omitted] [ABSTRACT FROM AUTHOR]

• The model can account for the non-linear lifting of the flange groove and the effects of wheelset traverse and side roll. • The wheel tread and flange are alternately loaded with two wheel load transition areas in the frog area. • Wear in the flange bearing area is significantly higher than in the tread bearing area, with an increase of 59.7%. • RCF damage dominates in the wing rail and the two wheelload transition areas. • Reducing the speed to 15 km/h significantly improves the service performance of the fixed frog. The tram No. 3 turnout fixed frog uses a variation in the depth of the flange groove so that the wheel rolls over the frog area in a continuous flange bearing. This method of travelling over the turnout requires the wheel load to transition back and forth between the tread and the flange, resulting in wheel-rail impact, which in turn affects service life. In order to investigate its service characteristics, this paper has established a transient wheel-rail rolling contact finite element model for the No. 3 turnout fixed frog. The macroscopic dynamic response and microscopic wheel-rail contact solution as the tram passes through the turnout at different axle weights and speeds are analysed in detail, and the changing patterns of wear and fatigue damage are investigated. The research shows that rail wear is particularly severe in the wheel flange bearing area, approximately 1.6 times greater than in the tread bearing area. In addition, when tram speeds are reduced to 15 km/h, there is a significant reduction in wheel-rail impact and wear, thereby improving ride smoothness and safety. The results of this study are of great significance to the operation and maintenance of the No.3 fixed frog turnout. [ABSTRACT FROM AUTHOR]

[Display omitted] Material microstructure plays a key role in crack initiation under rolling contact fatigue. When studying microstructure with crystal plasticity finite element method (CPFE), mesh sensitivity study is of great importance, as the surface-near region is under high uniaxial stresses. In this paper, a new structured mesh strategy is purposed and compared with the classical unstructured mesh strategy. Modelling tests on a bi-grain and a polycrystal model show the calculation of geometrically necessary dislocation (GND) density, recently proposed as a suitable fatigue damage indicator, is highly dependent on mesh morphology, when GND hotspots tend to appear near distorted elements even in homogeneous materials. With uniform mesh size and shape, structured mesh elements can provide physically more acceptable GND calculations, which is particularly important in loading scenarios with complex stresses, such as rolling contact fatigue. Computational efficiency is also improved compared to unstructured models because a smaller number of elements are required in a structured mesh model and pre-processing of the mesh is not required. [ABSTRACT FROM AUTHOR]

• Zig-zag morphology, grain refinement and secondary cracks are typical characteristics of zig-zag crack region. • The plastic deformation zone at the crack tip being limited to a few grain diameters caused the zig-zag morphology. • Grain refinement and secondary cracks formed during the severe pressing of crack. Shattered rim is a century-old problem that restricts the reliability of railway wheels in service. In this paper, the formation mechanisms of the zig-zag crack region on the shattered rim of railway wheel were investigated. First, the zig-zag crack region was observed using both scanning electron microscopy (SEM) and transmission electron microscopy (TEM) and was identified as a typical region for crack propagation in giga-cycle rolling contact fatigue behavior. The zig-zag crack bands have a height range of 3–30 μm, with an average of 13.4 μm, and a width range of 0–500 μm, with an average of 184.6 μm. The size values of band height and width are close to the values of the pearlite and protoaustenitic grain size. The formation of the zig-zag morphology in the zig-zag crack region is due to the periodic deflection of the propagation path relative to the initial propagation plane, which is a result of the limited plastic deformation zone at the crack tip that extends only a few grain diameters. The grain refinement and secondary cracks in the zig-zag crack region are attributed to the large compressive and shear stresses induced by the applied rolling contact loading. [ABSTRACT FROM AUTHOR]

The random arrangement of particle composition or the heterogeneity of the particles' inherent properties is what causes the variability of mechanical parameters in sandy soils. Combining the discrete element method with random field theory, a random discrete coupling modeling method is refined, in which a rolling resistance contact model was used to take into account the rolling friction characteristics of sand soil particles. Four random discrete element models (RDEM) are developed for typical working situations taking into account the two random field factors, i.e., the coefficient of variation and fluctuation range. The Monte Carlo method is employed to simulate the triaxial RDEM, and the stress-strain relations, parameters of strength and deformation are analyzed. The effects of the coefficient of variation (Cov) and fluctuation range (δ) on the variability of mechanical characteristics are studied. The results show that the mean shear modulus G , peak friction angle φ p , and critical friction angle φ c of random heterogeneous samples decline while the mean Poisson's ratio μ increases as the Cov increases. The mean values of parameters of deformation and strength of random heterogeneous samples eventually approach those of homogeneous samples as the δ increases. [ABSTRACT FROM AUTHOR]

• New insights on fractional thermoelasticity are provided using CF, AB and TC fractional derivatives. • Transient thermoelastic interactions between materials and a moving heat source are systematically studied. • The influences of different fractional derivatives on thermoelastic responses are compared. • The effects of fractional order and the velocity of heat source are studied under two sets of boundary conditions. • Time history of all responses is provided to show the effect of fractional derivative of long term process. Transient thermoelastic interactions between materials and the moving heat sources, i.e. Laser additive manufacturing, Laser-assisted thermotherapy, high speed sliding and rolling contacts, are becoming increasingly important. In this work, a unified fractional thermoelastic theory is developed, and applied to study transient responses caused by a moving heat source. Theoretically, new insights on fractional thermoelasticity are provided by introducing new definitions of fractional derivative, i.e. Caputo-Fabrizio, Atangana–Baleanu and Tempered-Caputo type. Numerically, a semi-infinite medium subjected to a source of heat moving with constant velocity is considered within the present model under two different sets of boundary conditions: stress free and temperature given for the first, displacement fixed and thermally adiabatic for the second. Analytical solutions to all responses are firstly formulated in Laplace domain, and then transformed into time domain through numerical method. The numerical results show that Caputo-Fabrizio and Atangana–Baleanu type models predict smaller transient responses than Caputo type theory, while Tempered-Caputo model may give larger results by increasing the tempered parameter. Meanwhile, the effect of fractional order, tempered parameter of Tempered-Caputo model, and the velocity of heat source on all responses is discussed in detail. The time history of responses shows that: for long-term process, the exponential function of TC definition will make sense, and the temperature from TC model is greatly different from that of C model. This work may provide comprehensive understanding for thermoelastic interactions due to moving heat source, and open up possibly wide applications of such new fractional derivatives. [ABSTRACT FROM AUTHOR]

The Performance of rolling element bearings has a significant influence on reliability and safety in the various engineering fields. While heading toward the condition evaluation of rolling element bearings, the higher dimensionality of feature space became a crucial concern. Thus, to have a check on the hurdles, this paper proposes a novel approach of bearing condition assessment utilizing Local mean decomposition (LMD) and spectral clustering (SC). Spectral Clustering (SC) is an influential tool, which heals the curse of dimensionality and facilitates the model by imparting a systematized structure. SC focuses more on connectivity rather than geometrical vicinity; moreover, the provision of a similarity matrix makes SC more reliable and increases its performance. To enrich the efficiency of SC, a novel decision criterion, PI (Parting Index) aiming the optimal number of clusters based on a new similarity indicator and disorder indicator coined as Synergic Association Index (SAI) and Separation Index (SI) respectively, has been proposed. The work aims to achieve better performance degradation assessment (PDA) by the application of the new SC-PI approach with the following steps; the first step is the decomposition of vibration signal into product functions (PFs) utilizing LMD; the second step involves the extraction of proper fault features; third, the extracted features are classified with the SC-PI method; finally the feature or attribute vectors are endowed to trained model and confidence value (CV) is calculated. The proposed method is validated on two datasets of different fault types. The results so obtained indicates that the SC-PI method easily differentiates the various stages when compared to different assessment techniques i.e. time-domain features, self-organizing map (SOM), k-medoids and Gaussian mixture model (GMM). • A novel method for performance degradation assessment is proposed. • LMD and SVD are employed to extract fault features. • An advancement to Spectral clustering with a novel method for the optimal number of clusters has been made to prepare an assessment modal and index. [ABSTRACT FROM AUTHOR]

• Bearing's cavitation effects can affect the rotor dynamic response. • Stability threshold is changed due to bearing cavitation effects. • Cavitation effects has low influence in normal operational conditions. This work evaluates the influence of the cavitation effects of hydrodynamic journal bearings on the rotating system dynamic response. Several simulations were performed in order to determine in which operating conditions the cavitation effects become relevant to the rotors dynamic behavior. The rotating system model is constructed by means of the Finite Element Method (FEM), in which the rotor is supported by hydrodynamic journal bearings. Two different approaches were used to model the journal bearing, being Gumbels condition used for analyses without conservation of mass in cavitation and Elrods cavitation algorithm for analyses with conservation of mass. The results show that the inclusion of conservation of mass in cavitation does not lead to significant changes in the rotors dynamic response under normal operating conditions. However, conditions near to the instability threshold show a significant difference in dynamic response, since the model without conservation of mass reaches this limit before the model that includes these effects. [ABSTRACT FROM AUTHOR]

Previous investigations have shown that load carrying capacity of gears manufactured by wire EDM is three times higher than ground gears for short time contact fatigue tests. Typical EDM surfaces are characterized by discharge craters, which lead to beneficial running-in topography formation. Investigations of tooth flank load-carrying capacity of specimen represent the tribological performance of rolling contacts. In gear testing, a tribological comparable disk-on-disk test is performed to reduce effort and costs during machining gears with complex geometries. For this purpose, testing shafts with high geometrical accuracy and different surface qualities were manufactured by wire EDM on a single-axis rotary indexing table. Following, the surface integrity and performance of these specimens on the disk-on-disk test were investigated focusing on short time contact fatigue strength and running-in behavior. [ABSTRACT FROM AUTHOR]

During the operation of freight cars, uneven wear occurs in the central bowl of the rail truck bolster. This article aims to determine the concentration of the filler of the composite material to reduce the wear of the central bowl of the rail truck bolster. In this work, for the first time, a mathematical model of the distribution of the filler concentration in the projected composite tape was obtained. To reduce the wear of the working surface of the central bowl of the rail truck bolster, as well as to ensure uniform wear distribution, it is proposed to weld a composite tape with variable tribomechanical properties using contact welding. The wear value of the working surface of the central bowl of the bolster of the rail truck bolster when using composite tapes of compositions Fe-Cr-Ni-Cr 3 C 2 and Fe-Cr-Ni-TiC with contact welding was 0.15–0.18 mm per 10,000 km - for a loaded freight car and 0.08–0.10 mm per 10,000 km for an empty freight car. According to the amount of wear, the value of the service life of the center plate assembly is predicted, which is 320,000–420,000 km. [ABSTRACT FROM AUTHOR]

In this paper, the temperature-transformation finite element model of low carbon bainitic steel Q690D was established based on the characteristics of controlled cooling after rolling. In the process of controlled cooling after rolling, there are many factors that affect the temperature in the direction of the thickness of the steel plate, mainly from the thickness of the steel plate, cooling water flow, open cooling temperature and cooling water collection tube opening method analysis. The effect of different factors on the cooling rate is analysed by simulation to obtain the corresponding variation of temperature in the thickness direction. The results show that the greater the thickness, the less effective the energy transfer to the surface layer. This means that thinner steel plates are easier to control in terms of temperature. The temperature drop in the thickness direction is relatively large when using the mode with upper and Upper and lower spray volume ratio of (650/1000) for the DQ section and Upper and lower spray volume ratio of (500/1000) for the ACC section, and the reasonable range is easier to be obtained. On the premise of not being affected by the cooling rate of temperature drop, in the thickness direction, the latent heat value of phase change is different due to the different time periods of phase change, and the heat generated in each microstructure is different, so the temperature distribution shows that the starting cooling temperature of 860 °C is more gentle and uniform in the temperature slope than the starting cooling temperature of 750 °C. Among the four header opening modes, mode (1111111110000011111) makes the temperature of each layer of the steel plate more uniform and reasonable, superior to the continuous opening mode. [ABSTRACT FROM AUTHOR]

• A 3D wheel-rail rolling contact FE model was established based on measured corrugation and hardness distribution of rails. • The effect of uneven hardness distribution on the stress-strain distribution within the wheel-rail contact area was analysed. • The wheel-rail rolling contact behaviour in the corrugation zone changes significantly after work hardening. • Work hardening has a major effect on the difference in wear between the crest and the trough. The process of work hardening in the corrugation zone of the steel rail results in an uneven distribution of hardness, with higher hardness in the corrugation troughs and lower hardness in the corrugation crests. To study the influence of hardness on the rolling contact behavior of the wheel-rail at corrugation zone, a three-dimensional wheel-rail transient rolling contact finite element model is established based on the measured corrugation and hardness distribution of the rail to reveal the influence of the non-uniform distribution of hardness at corrugation zone on the wheel-rail contact state and the wear and fatigue of the rail surface. The results indicate that: (1) work hardening in the corrugation zone leads to an increase in equivalent stress and strain within the contact patch between the wheel and rail. However, due to the increase in yield strength, plastic deformation and residual strain are somewhat reduced; (2) The uneven distribution of hardness in the corrugation zone results in an elevation of longitudinal shear strain between the wheel and rail, which may initiate tangential fatigue cracks and spalling of the steel rail surface; (3) the wear on the rail surface is large near the wave crest and small near the wave trough, work hardening will change the wear difference between the wave crest and wave trough while reducing the wear, resulting in the "peak shaving and valley filling" phenomenon developing faster in the early wave wear period and slower in the later period. [ABSTRACT FROM AUTHOR]

Wheel and rail profiles have significant impacts on the vehicle system dynamics. Improper wheel and rail profiles lead to the decay of vehicle dynamics performance, hunting instability and derailment. In this study, we propose a model, stacking feature deep forest, to determine the limit wheel profile for hunting instability using wheel/rail geometric contact parameters. We calculate the critical speed of the vehicles under various wheel and rail profiles and record their wheel/rail geometric contact parameters as samples. Two experiments are conducted. One is the binary classification aiming to identify whether the wheel/rail geometric contact parameters guarantee the vehicle's critical speed is higher than the threshold of its operational speed. The other is the multi-classification to determine the interval of the critical speed. The results show the stacking feature deep forest achieves an accuracy of 85.10% on the test set which is higher than other popular ensemble models. However, all models' accuracy is lower than 70% in multi-classification. The Shapley additive explanations are utilized to enhance the explainability of the stacking feature deep forest. The Shapley additive explanation importance reveals that the equivalent conicity of 1 mm has the most impact on hunting. Its importance is 1.32 times more than the equivalent conicity of 3 mm. Nevertheless, the equivalent conicity of 3 mm is nearly positively correlated to the hunting probability and this characteristic is suitable as a qualitative criterion. • Stacking feature deep forest has the best performance in determining the limit WRGCPs. • Equivalent conicity at 1 mm have the most significant impact on hunting. • The relationship between equivalent conicity of 3 mm and hunting is more straightforward. • A single or a few WRGCPs cannot provide reliable hunting movement prediction. [ABSTRACT FROM AUTHOR]

• The behavior of the rail fastening system on slab track at railway bridge ends is investigated. • The stiffness modeling method of the rail fastening system is an important factor of the serviceability evaluation. • The actual nonlinear behavior of the rail fastening system can cause a large upward displacement. • The nonlinear behavior of the rail fastening system should be considered to predict the forces acting on the rail fastening system at the railway bridge ends. Rail fastening systems on a slab track at railway bridge ends are often damaged, which increases the maintenance costs. The serviceability evaluation of a rail fastening system on a slab track at railway bridge ends is based on the assumption that the stiffness of the rail fastening system is linear. The behavior of the rail fastening system on slab track at the railway bridge ends is studied in detail in this study. In the experimental model, the abutment and pier of the railway bridge were considered to be directly connected to two H-beams through a rail and rail fastening systems. A stiffness model of the rail fastening system for the finite-element analysis was established by performing a clamping-force test. In the finite-element analysis, the rail fastening system was considered as both linear and nonlinear stiffness models. The experimental and numerical results were very similar when the rail fastening system was considered as the nonlinear stiffness model. With the same uplift force acting on the rail fastening system, the displacement results of the nonlinear stiffness model were larger than those of the linear stiffness model. Therefore, it is necessary to employ the nonlinear behavior of the rail fastening system and investigate a displacement-based design method of the rail fastening system when evaluating the serviceability of the rail fastening system on the slab track at railway bridge ends. [ABSTRACT FROM AUTHOR]

This paper presents a case study in sliding/rolling contacts between steel components operating in packaging devices for powder pressing, where the non-conformal contact involving a rotating roller (AISI M2 tool steel) and pins (AISI 440B martensitic stainless steel) led to the formation of macro- and micro-pitting on both mating surfaces. On the basis of metallurgical failure analysis, surface-origin contact fatigue was identified as the main damage mechanism. Microstructural stress raisers such as relatively large carbides, clustered along plastic flow lines, were observed in both steels. A white etching layer (WEL), due to severe sliding/rolling conditions, further enhanced the formation of surface-origin cracks on the roller. Unlabelled Image • Failure analysis of steel roller and pins after field operation. • Morphological and microstructural evaluation of the damaged surfaces. • Surface-origin cracks due to contact fatigue as main cause of damage. • Identification of microstructural stress raisers influencing the contact fatigue behavior. [ABSTRACT FROM AUTHOR]

• A vibration prediction model of long-span steel truss cable-stayed bridge was established, and validated by test results. • The vibration reduction mechanism of damping pad floating slab (DPFS) on the long-span steel truss cable-stayed bridge was analyzed in this paper. • The vibration reduction effect of the damping pad floating slab (DPFS) on the long-span steel truss cable-stayed bridge was discussed in this paper. With the development of urban rail transit, long-span steel truss cable-stayed bridges have become increasingly favored. Therefore, train-induced bridge-borne vibration and noise are occurring more often. The damping pad floating slab (DPFS) has been widely used as an effective vibration damping track structure; however, there is a lack of research on the vibration mechanism and effects of the DPFS for long-span steel truss cable-stayed bridges. This study focuses on the steel truss cable-stayed bridge in urban rail transit. First, the theoretical model of the train-track-bridge coupling interaction is established in the frequency-domain (the track structure is DPFS, and the interaction of multiple wheels is considered). Using this model, the wheel–rail dynamic force, force transmission rate of the track, and the force transmitted to the bridge are calculated. Then, the vibration prediction model of the long-span steel truss cable-stayed bridge is established using the plate-beam finite element (FE) method and statistical energy method. The force transmitted to the bridge is applied to the vibration prediction model to obtain the vibration transmission characteristics of the typical plate of the bridge. The prediction model is verified by comparing the obtained results with the field test of a long-span steel truss cable-stayed bridge, and the damping mechanism of DPFS track is discussed. Finally, the force transmitted to the bridge is calculated based on the embedded-sleeper (ES) track structure (the ES has no vibration damping facilities). The values of the overall vibration level are calculated from the prediction models using ES and DPFS, and the vibration reduction effect of DPFS is studied by comparison with the ES. [ABSTRACT FROM AUTHOR]

The formation of White (WEL) and Brown Etching Layers (BEL) on rail raceways during service causes the initiation of microcracks which finally leads to failure. Detailed characterization of the WEL and the BEL in a pearlitic rail steel is carried out from micrometer to atomic scale to understand their microstructural evolution. A microstructural gradient is observed along the rail depth including martensite, austenite and partially dissolved parent cementite in the WEL and tempered martensite, ultrafine/nanocrystalline martensite/austenite, carbon saturated ferrite and partially dissolved parent cementite in the BEL. Plastic deformation in combination with a temperature rise during wheel-rail contact was found to be responsible for the initial formation and further microstructural evolution of these layers. The presence of austenite in the WEL/BEL proves experimentally that temperatures rise into the austenite range during wheel-rail contact. This is in agreement with finite element modelling results. Each wheel-rail contact must be considered as an individual short but intense deformation and heat treatment cycle that cumulatively forms the final microstructure, as shown by diffusion length calculations of C and Mn. The presence of secondary carbides in the BEL indicates that the temperature in the BEL during individual loading cycles reaches levels where martensite tempering occurs. Partially fragmented primary cementite laths, enriched in Mn, depleted in Si, and surrounded by a C-gradient and dislocations were found in the BEL. The initial step in the formation of BEL and WEL is the defect- and diffusion-assisted decomposition of the original microstructure. Image 1 [ABSTRACT FROM AUTHOR]

Abstract RCF tests were conducted on bearings lubricated with three different lubricants: a gearbox oil, a MAC fluid and PFPE oil. The decomposition of the MAC fluid and PFPE was investigated by FTIR and NMR. Gearbox oil tests showed flaking and networks of subsurface cracks with partial intercrystalline crack growth. Cross-sectional analysis revealed the formation of WEAs. FEM correlated the damage with stress fields. The results of the MAC lubricated tests showed surface flaking and intercrystalline crack growth in the subsurface. The PFPE lubricated bearings showed no signs of hydrogen induced damage. Post-experimental hydrogen analysis of the bearings indicated an increased hydrogen concentration in the samples lubricated with the gearbox oil and MAC compared to those lubricated with PFPE. Highlights • Post RCF hydrogen analysis showed concentration variation with various lubricants. • Hydrogen evolution in RCF tests was associated with lubricant decomposition. • The levels of hydrogen in bearings was correlated with damage telltale signs. • Failure patterns were correlated to stress fields obtained from FEM. [ABSTRACT FROM AUTHOR]

Abstract Gear oil of heavy mining machineries are designed to provide anti-wear and anti-friction protection under extreme load condition. In present study thermophysical and tribological properties of industrial gear oil with nanoparticles additives (Al 2 O 3 and SiO 2) has been experimentally evaluated. Morphology of dry nanoparticles under FE-SEM shows that both nanoparticles are spherical. DLS test shows the presence of mild-agglomeration of nanoparticles in the dispersion. Density and viscosity of nanolubricants is tested with varying temperature and particle volume fraction. Measured viscosity results for Al 2 O 3 /gear oil nanolubricants follow the existing empirical model and new model has been proposed for SiO 2 /gear oil nanolubricants. Anti-friction and anti-wear properties of nanolubricants are tested on pin-on-disc test apparatus. FE-SEM and energy dispersive spectroscopy (EDS) analysis of wear scar (pin SS-304), evident the occurrence of ball bearing and surface polishing effects, which may be responsible for advanced tribological properties of the oil. Test results reveals that ball bearing have dominating effect in enhancement of tribological performance. Graphical abstract Image 1 Highlights • Enhancing the tribological performance of the gear via Al 2 O 3 and SiO 2 nanoparticles. • Correlation proposed for the viscosity of gear oil nanolubricant. • Pin-on-disc tribotester displayed 25% and 22% improvement in anti-friction property with 0.3% Al 2 O 3 and SiO 2 nanoparticles. • FESEM and EDS analysis of wear scar reveals the dominance of ball bearing effect over surface polishing effect. [ABSTRACT FROM AUTHOR]

Highlights • A 3D FE dynamic interaction model is proposed to simulate wheel-rail squeal-exciting contact. • The squeal-exciting contact is investigated with considerations of dynamic effects, unsteady lateral creepage and velocity-dependent friction. • Continuum and structural dynamics are included in the solution of frictional rolling contact. • Large-creepage-induced waves which share features with Rayleigh wave are discovered. • Two widely accepted generation mechanisms of frictional instability can be tackled by the model. Abstract Complex frictional rolling contact and high-frequency wheel dynamic behavior make modeling squeal greatly challenging. The falling-friction effect and wheel mode-coupling behavior are believed to be the two main mechanisms that generate unstable wheel vibration and the resulting squeal noise. To rigorously consider both mechanisms in one model, we propose an explicit finite element (FE) model to simulate wheel-rail dynamic frictional rolling. Wheel-rail squeal-exciting contact is investigated with considerations of dynamic effects, unsteady lateral creepage and velocity-dependent friction. With the inclusion of the dynamic effects in the contact solution, large-creepage-induced waves, which share features with Rayleigh waves, are discovered. The solutions of the dynamic contact calculated using the proposed model indicate that the explicit FE method is able to reproduce the falling-friction effect. The transient analyses of wheel-rail frictional rolling with wheel lateral creepage show the coupling of the axial and radial dynamics of the rolling wheel model, suggesting that the explicit FE method can also reproduce the mode-coupling behavior. This study improves the understanding and modeling of squeal-exciting contact from the perspective of wheel-rail dynamic interaction. Graphical abstract Image, graphical abstract [ABSTRACT FROM AUTHOR]

Abstract Due to the improvement of the wear property, rolling contact fatigue including shattered rim and shelling are the main failure causes of the high-speed railway wheels. In this paper, shattered rim and shelling occurred on the service wheels of the China Railway High-speed (CRH) trains were systematically investigated. The recorded data of the last ten years CRH operation indicated that all shattered rims and shelling were detected with serving >106 km (corresponding to the fatigue life 107–109 cycles) which is very-high-cycle fatigue (VHCF). The crack initiation region of shattered rim located at the depth of 10–25 mm from the tread, while that of shelling located at the depth <10 mm from the tread. The VHCF features under rolling contact loading were observed on the opening crack surfaces, i.e., similar VHCF features in uniaxial loading including the defect, fish-eye, and crack propagation region and unique VHCF features of the three dimensional crack surface feature, beach bands uniformly distributed in the crack propagation region, absence of fine granular area (FGA). The VHCF model considering the stress distribution, defect size and hardness were applied to discuss the failure mechanism of the shattered rim and shelling. Highlights • The shattered rim and shelling are caused by very-high-cycle fatigue (VHCF) under rolling contact loading. • Unique features were presented in the crack initiation region of VHCF under rolling contact loading. • The multi-axial stress distribution, the large defect, the hardness distribution are responsible for the VHCF behavior. [ABSTRACT FROM AUTHOR]

• A first study of the effect of full creepage on RCF crack growth behaviour. • Predicted crack growth directions show a good agreement with field observation. • Lateral and spin creepages can significantly affect K II and K III evolutions. • Increase in spin creepage is more detrimental to RCF crack driving force. In heavy-haul railway systems, the experience of high traction force of rails in curved tracks significantly accelerates the rolling contact fatigue crack growth. The overall level of traction force and its detailed distribution within a contact patch can be determined by the extent of wheel slips in different directions, also referred to as creepage. However, few studies have focused on quantifying the influence of creepage on rolling contact fatigue crack growth behaviour. In this paper, a numerical method is proposed to investigate the non-proportional mixed-mode rolling contact fatigue crack growth behaviour in the presence of severe longitudinal, lateral and spin creepages. To partially validate the proposed numerical method, the predicted crack growth directions on the rail surface are compared with the cracking patterns obtained from field observations. A parametric study is also conducted to further quantify the influence of different creepage combinations on the evolution of stress intensity factors at the crack front. Results show that both lateral and spin creepages can significantly affect the phase and maximum magnitude of K II and K III during one complete loading cycle. Moreover, the increase of spin creepage is found to have a more detrimental effect on overall RCF crack driving force than the increase of the other two creepage components. [ABSTRACT FROM AUTHOR]

[Display omitted] • A dislocation-based model with a robust convergence is developed to investigate the contact problems. • A deterministic method is proposed to progressively evaluate the stick and slip contact conditions of crack faces. • The slip accumulation of crack faces during the loading process is accounted for the description of friction evolution. • The effects of friction coefficient, crack alignment and location on the shear behaviors of crack faces are analyzed. Mechanical transmission components are generally under the risk of contact fatigue, resulting in cracks initiated from the subsurface. When subject to compressive stress, these cracks might be forced to be closed, thus their faces are in partial slip contact. Under such conditions, the interactions of stick and slip zones cannot be directly determined, which is one of the greatest challenges of contact fatigue problems. In this study, the distributed dislocation technique is adopted to investigate the stick–slip friction along the alignment of shear cracks in arbitrary orientations in a half-plane under contact loading. The unknown dislocation density describing the crack face displacement is iteratively calculated based on the stress conditions and then introduced to update the surface gap between contacting bodies. The complex expressions of the influence coefficients used to determine the stress and displacement induced by the dislocations are derived and the FORTRAN codes are provided in the Supplementary Materials. A step-by-step loading method is proposed to progressively capture the slip history of crack faces. The model is also capable of simulating rolling contact problems. The results are comparable to those predicted using the finite element method with more robust convergence properties. The effects of friction coefficient, crack alignment, and locations of crack faces are discussed in detail. The model paves the foundation for further studies on competing mechanisms of crack propagation and crack face wear, and provides insights into the frictional fracture of materials under contact loading. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ultrasonic rolling and its finite element simulation on a bearing raceway was conducted. • Multi-objective process optimization for ultrasonic rolling on a bearing was performed. • Oriented martensitic grain stacking forms a flocculent plastic deformation layer. • Carbide particles are refined, and its size changes gradiently along the layer depth. For the first time, the ultrasonic surface rolling processing (USRP) technology was applied to a real bearing raceway, and a finite element simulation model for USRP on a bearing raceway was established. Practical tests were conducted to evaluate the surface integrity of the bearing raceway before and after USRP treatment. The USRP parameters were optimized using Taguchi-gray correlation analysis. The results show that the optimal process parameters for the 7224 bearing raceway are: an amplitude of 10 μm, a static pressure of 2400 N, a spindle speed of 45 rad/min, and rolling times of 7. In the process of USRP, residual compressive stress results from inhomogeneous elastic and plastic deformation. Adjacent tempered martensitic laths merge and deflect at a certain angle along the rolling direction to form directional grain stacks, resulting in a flocculent plastic deformation layer. The USRP based on the finishing mechanism of "peak-cutting and valley-filling" can improve the surface micro-morphology, reduce roughness value Ra to approximately 0.16 μm, and effectively eliminate microscopic cracks caused by grinding. The micro-hardness of the bearing raceway surface increased from 760 HV to 840 HV under the dual action of surface grain refinement and work hardening effect. [ABSTRACT FROM AUTHOR]

• Bearing model considering cryogenic fluids and solid lubrication was developed. • Effect of fluid loads and spinning behaviors on bearing power loss was explored. • Hydraulic drag force is the main cause of ball-inner ring skidding at high speeds. • Ball-raceway spinning power loss dominates under high axial preload conditions. Ball bearings in liquid rocket turbopumps usually generate a large amount of power loss as they operate under extreme conditions, including cryogenic fluids, solid lubrications and extra high loads and speeds. However, to explore the power loss mechanism, a bearing theoretical model considering the influence of cryogenic fluid and solid lubricant is needed. In this paper, by introducing the newly developed fluid resistance forces and the rolling contact traction model into the equilibrium equations of the bearing, a new fluid-structure interaction-based quasi-static model is proposed, which can well simulate the rolling-sliding behaviour of balls under solid lubrication conditions. Based on tribology and kinematic analysis, eight power loss components of the bearing are deduced. The proposed model is validated by comparison with both experiments and existing theoretical methods. The results show that sliding, spinning and hydraulic power losses are the most important components of the bearing. Moreover, tribological behaviour, including creeping, skidding and spinning of the ball, is a key factor affecting the distribution of the power loss components. Utilizing the proposed model, the proportion of load-dependant power loss can be optimized to improve the anti-wear and heat-resisting properties of cryogenic ball bearings. [Display omitted] [ABSTRACT FROM AUTHOR]

This paper describes development of equations for linear elastic stress analysis of concentric shims (reinforcements) in spherical multilayer bearings under general three-dimensional loading and uniform temperature change. The theory is based on a generalization of thin shell theory and the Complementary Strain Energy Principle. Some examples are given to illustrate the shim stresses due to direct loading from the rubber pads and their agreement with finite element predictions. This loading is found using the linear elastic pad and bearing analysis in (Schapery, 2018). Although the shims are assumed perfectly rigid in the pad and shim analyses, the total strain energy in the shims can be found using their Young's modulus and Poisson's ratio, enabling estimation of the effect of shim deformation on bearing stiffness. These analytical models for pads and shims are intended to assist in rapid preliminary design of elastomeric bearings when utilized, for example, in a Mathcad computer program embedded in Excel that the author used. Final designs can be done with finite elements to account for rubber nonlinearity and shim deformation. [ABSTRACT FROM AUTHOR]

The aim of present study is to monitor the delamination failure of plasma sprayed Al 2 O 3 –40 wt% TiO 2 composite ceramic coating (AT40 coating) in rolling contact condition by acoustic emission (AE) technology. The AE signals of the delamination failure process were divided into three types (type I: normal contact; type II: fatigue crack initiation; type III: delamination failure) based on the feature of AE count. The waveforms and frequency spectrums of different types of AE signals during delamination failure process of the coatings were obtained by Empirical mode decomposition (EMD) method. The relationship between the waveform/frequency of the AE signals and the delamination failure mechanism of the AT40 coatings were discussed in detail. [ABSTRACT FROM AUTHOR]

Pitting is frequently encountered in machine elements, such as bearings, cams and gears, containing parts in relative sliding-rolling motion. Most of investigations on rolling contact fatigue have been carried out by means of numerical/analytical models in the frame of LFEM, but the interpretation of the numerical results is still controversial. The SIFs history is highly non-proportional and the intensity of the peaks is not expected to cause propagation, since they do not exceed the fatigue threshold usually found for long cracks in steels and cast irons. To shed light on this issue, this work is intended to reproduce experimentally the SIF-cycles, estimated by our previous model of RCF crack, by using an alternative non-standard procedure. The novel experimental apparatus is based on the exploitation of a kinked edge crack subjected to a compressive load distributed through the thickness. Changing the load position and intensity permits to induce different values and ratios of SIFs. It has been found that lubricant is strictly necessary to trigger crack propagation, which can be in form either of coplanar extension followed by branching or of branching only. Coplanar extension occurs when mode II SIF range exceeds a certain threshold, well below the typical fatigue threshold. Empirical evidences are in accordance with the tendency of the RCF cracks to do coplanar extension and to branch into the bulk material and toward the surface. Coplanar extension is more pronounced in the interior of the sample, while branching occurs only at the edges. The results indicate that our previous modelling of RCF crack is likely to underestimate the effective SIFs. Thus this work would open the way to improve the actual understanding and modelling of RCF. [ABSTRACT FROM AUTHOR]

A theoretical and numerical framework to evaluate rolling contact using a Lagrangian formulation in the sense of continuum mechanics is established. The treatment corresponds to a non-stationary and large deformation model that takes into account all inertial effects. A finite element formulation is implemented featuring cylinder-plate contact. The unilateral contact of hyperelastic and viscoelastic rolling wheel on a rough foundation on which friction laws hold is characterized by a highly nonlinear variational inequality. The solutions might predict the dependence of stress distribution with viscous properties. A parametric study shows the maximum power dissipation as a function of velocity, coefficient of friction and viscosity parameter. [ABSTRACT FROM AUTHOR]